DNS Switcharoo.

Ok, here's the setup:

Domain Controller/DNS Server 1 (At Office) (Server 2008 R2)
Domain Controller/DNS Server 2 (At Datacenter) (Server 2008 R2)
Domain Controller/DNS Server 3 (At Datacenter) (Server 2012)

When anyone here at the office runs ipconfig /all it will show DNS like this:

DNS Servers........... : DNS Server 1 IP Address
                                  DNS Server 2 IP Address

Issue: We want to retire DNS Server 2 and use DNS Server 3 in its place. DNS Server 1 and DNS Server 3 are already pointed at each other. The goal is to have everyone's ipconfig /all to look like this:

DNS Servers........... : DNS Server 1 IP Address
                                  DNS Server 3 IP Address

We want to pull DNS from 1 & 3 and not 1 & 2 like it is now. I believe fixing this problem means going into DNS Server 1 and adding 3 as a host and deleting 2 from DNS. I'm not sure step by step how to do this, though and/or what I need to do on 2 & 3. Any help on proper way of pointing 1 at 3 so we all pull from 1 & 3 is greatly appreciated.